MRDS - Mineral Resource Data System, where you can get GPS data for mines around the country, down to the county. The data can be exported in several formats, including Google Earth's KML format. That can be converted to a file that you can then import into your handheld GPS for out in the field. There is free software that does this, calledGPS Babel. This way you can plan a trip to a certain area, download mine locations to Google Earth, weed out the mines you aren't interested in, save a KML file, and convert it to the file format for your GPS device. Then use your GPS device's software to import the data to your handheld GPS receiver.